A motor-vehicle engine system may include a vacuum pump to evacuate air from one or more motor-vehicle components. Such components may include a vacuum servo booster for hydraulic brakes, a throttle driver, or an actuated damper in the ventilation system of the vehicle, for example.
The vacuum pump of a motor-vehicle engine system is typically a rotary-vane type positive-displacement pump. International Patent Publication Number WO2007/003215A1 shows one example of this type of pump. The pump includes a single-vane rotor that rotates within a stator and divides the interior volume of the stator into non-communicating chambers. Such chambers include an inlet chamber and an outlet chamber. The stator has an inlet passage that communicates with the inlet chamber, and an outlet passage that communicates with the outlet chamber. The rotor and stator are coated with a film of lubricant oil and configured so that each rotation of the rotor increases the volume of the inlet chamber and decreases the volume of the outlet chamber. Accordingly, air is admitted through the inlet passage and expelled through the outlet passage, providing the basic function of the vacuum pump. In this pump and others like it, a discrete non-return valve may be coupled to the outlet passage to minimize the amount of air that re-enters the pump at the beginning of each pumping cycle. The non-return valve may include a flexible, spring-loaded shutter, or reed-type element.
During operation of the vacuum pump, the spring-loaded shutter starts to open when the pressure in the outlet chamber overcomes the restoring (closing) force of the shutter. The inventors herein have found that the limited opening extent of the shutter, together with its somewhat large restoring force, results in excessive lubricant oil pressure in the outlet chamber at the end of each pumping cycle. Under some conditions, the high pressure of the outlet chamber relative to the inlet chamber causes misalignment or rocking of the rotor. This, in turn, may cause the rotor to impact the stator, resulting in objectionable noise from the vacuum pump.
Accordingly, one embodiment of the present disclosure provides a rotary-vane vacuum pump comprising a stator and a vaned rotor. The stator partly defines an outlet chamber and includes an outlet passage opening to the outlet chamber. The rotor is rotatably sealed to the stator. The rotor has a sealing area to block the outlet passage, and, an unsealing area alignable with the outlet passage by rotation of the rotor to periodically unblock the outlet passage. The disclosed pump offers reduced resistance to lubricant oil discharge from the outlet passage, which results in lower differential pressure between inlet and outlet chambers at the end of the pumping cycle. Therefore, the rotor is not subjected to misalignment or rocking forces that could result in objectionable noise from the pump.
The summary above is provided to introduce a selected part of this disclosure in simplified form, not to identify key or essential features. The claimed subject matter, defined by the claims, is limited neither to the content of this summary nor to implementations that address the problems or disadvantages noted herein.